This invention relates generally to field activated display sheets and more particularly concerns a field activated display sheet which utilizes both an electric field and a thermal field to activate twisting-ball displays, such as gyricon displays and the like.
Typically, a display device, in sheet form, comprises a thin sheet, which has many attributes of a paper document. It looks like paper, has ambient light valve behavior like paper (i.e. the brighter the ambient light, the more easily it may be seen), is flexible like paper, can be carried around like paper, can be written on like paper, can be copied like paper, and has nearly the archival memory of paper.
There have been different approaches to making a field induced display sheet such as U.S. Pat. No. 4,143,103 titled xe2x80x9cMethod of Making a Twisting Ball Panel Displayxe2x80x9d, in which the display sheet utilizes an elastomer substrate containing an array of addressable elements sandwiched between two electrode layers. The conductors of the first electrode layer are oriented orthogonally relative to the conductors of the second electrode layer. An addressable element is rotated upon application of an electric field between opposing conductors.
An alternate approach was disclosed in U.S. Pat. No. 5,717,515 titled xe2x80x9cCanted Electric Fields for Addressing a Twisting Ball Displayxe2x80x9d, having an array of addressable elements, with each array element including at least one spheroidal rotational element. A preferred direction of orientation is selected for rotational elements of a selected array element, with the direction of orientation forming an angle with a vector normal to a planar portion of the substrate surface in the vicinity of the selected array element. Rotational elements of the selected array element are aligned with the preferred direction of orientation by applying an electric field in the vicinity of the selected array element. The electric field has an electric field vector oriented parallel to the selected preferred direction, thereby causing rotational elements of the selected array element to rotate so as to align with the preferred direction of orientation.
Multithreshold addressing was disclosed by U.S. Pat. No. 5,739,801 titled xe2x80x9cMultithreshold Addressing of a Twisting Ball Displayxe2x80x9d, in which electrically and optically anisotropic spheroidal rotational elements have at least two different rotation thresholds. The spheroidal rotational elements are disposed in an elastomer substrate together with an addressing electrode assembly. The addressing electrode assembly allows a preferred region of the substrate to be selected in which at least one rotational element of the first set and at least one rotational element of the second set are disposed. A first and second electric field are applied to the selected region, with each of the first and second electric fields extending throughout the region. The first field caused rotation of rotational elements of both the first and second sets of rotational elements in the region. The second electric field facilitates rotation of rotational elements of the second set, without causing further rotation of any rotational element of the first set.
Although these approaches, utilizing a standard vertical electric field, are useful, it is desirable to improve on their performance. Accordingly, it is an object of this invention to provide a means for more effectively moving material within electric paper pixels than is possible with a standard vertical electric field, while improving bistability. Bistability is defined herein as maintenance of an image formed by an electric field for a suitable period of time after removal of the electric field.
Briefly stated, and in accordance with one aspect of the present invention, there is disclosed a display material for use in an electric paper system. The material includes two opposing outer surfaces, between which is disposed a plurality of optically and electrically anisotropic elements suspended in a substance capable of being liquified. A rotatable disposition of each element is achievable while the element is suspended in the substance and the substance is liquified.